Walter Adams was born in Syria, the son of American missionaries. After receiving his bachelor's degree at Dartmouth College, he accompanied his astronomy professor, Edwin B. Frost, to Yerkes Observatory, where he began graduate study. After two years there and one more year of study at Munich, he was summoned by his Yerkes director, George Ellery Hale, to help establish the Mt. Wilson Solar Observatory. There he served first as Hale's deputy and later as director from 1923 to 1945. His spectroscopic studies of the sun, done with Hale and others, led to the discovery that the sunspots are regions of lower temperatures and stronger magnetic fields than their surroundings. Turning to the stars, he made the discovery, with Arnold Kohlschütter, of a spectroscopic method for determining stellar distances: they showed that the relative intensities of spectral lines could be used to determine absolute magnitudes of both giant and main sequence stars. Adams used photography to measure the differential rotation of the sun. He shared with Theodore Dunham, Jr. in the discoveries of carbon dioxide in the atmosphere of Venus and the molecules CN and CH in interstellar gas clouds. Adams identified Sirius B as the first white dwarf star known, and his measurement of its gravitational redshift was taken as confirming evidence for the general theory of relativity. In retirement he continued his research at the Hale Solar Laboratory in Pasadena, California.